The present application relates generally to an air belt and air belt apparatus configured such that a bag-shaped belt is expanded by gas supplied from an inflator so that an occupant of a motor vehicle is kept under restraint when the motor vehicle encounters a crash or the like.
Japanese Unexamined Patent Application Publication No. 11-255057 provides an example of a conventional air belt and air belt apparatus.
As shown in FIG. 2, an air belt apparatus is provided that keeps an occupant under restraint in a front right seat 1. The air belt apparatus is provided with a retractor for a shoulder belt provided at a lower part of a center pillar 2, a retractor for a lap belt provided at a lower side of the retractor for the shoulder belt, a shoulder belt 6 being withdrawn from the retractor for the shoulder belt and extending through a slip guide 5 provided at an upper part of the center pillar 2, a lap belt 7 that is withdrawn from the retractor for the lap belt 4, a tongue device 8 being fixed to each of ends the shoulder belt 6 and the lap belt 7, a buckle device 9 being fixed to a seat base 10 that is composed of a seat frame or a slide rail, to which the aforementioned tongue device 8 is combined, and an inflator 11 being integrally formed with the buckle device 9.
The retractor for the shoulder belt and the retractor for the lap belt respectively retract the shoulder belt 6 and the lap belt 7 in a manner that allow the shoulder belt 6 and the lap belt 7 to be withdrawn. When an acceleration sensor does not detect acceleration greater than a predetermined value, such as during normal operation, the retractor for the shoulder belt and the retractor for the lap belt permit the belts 6, 7 to be withdrawn, thereby permitting movement of an occupant's body. On the contrary, when the acceleration sensor detects an acceleration of not less than the predetermined value, such as in the event of a crash or the like for the motor vehicle, both the retractor for the shoulder belt and that for the lap belt are configured to lock both the belts, 6 and 7, so that they are unable to be withdrawn and the occupant is kept under restraint. When the acceleration sensor detects the acceleration not less than the predetermined value, propellant is ignited and the inflator 11 generates high-pressure gas by means of combustion of the propellant.
The lap belt 7 is formed of a conventional flat-woven belt made of synthetic resin. On the other hand, part of the shoulder belt 6, which is in contact with a chest region of the occupant, is composed of a cylindrically shaped expandable bag 12 and a webbing 13 that generates tension force in the event of the crash of the motor vehicle while covering an outside of the bag 12. The shoulder belt 6 has a flattened belt-like shape during normal operation. However, when gas is supplied to the bag 12 from the inflator 11 the shoulder belt 6 is expanded and softly keeps the occupant under restraint. When the webbing 13, which is formed by warp knitting, is stretched out in a radial direction due to the expansion of the bag 12 the webbing 13 is contracted in a longitudinal direction, thereby applying an initial tension force to the shoulder belt 6.
FIG. 3 illustrates a cross-section of the shoulder belt 6 in a non-expansion state with the bag 12 being folded back in a switchback-like manner. The bag 12 is integrally formed with the webbing 13 by stitching thread 28 that is easy to rupture.
Because the bag 12, which is in the folded back state, is integrally formed with the webbing 13 by stitching thread 28, the folded state of the bag 12 is maintained and movement of the bag 12 relative to the webbing 13 is prevented. As a result, shoulder belt 6 is formed in a regular flattened shape and the softness of the shoulder belt 6 is maintained. Therefore, the feeling of the shoulder belt 6 is good and the sense of discomfort perceived by the occupant is alleviated. In the event of a crash of the motor vehicle, the stitching thread 28 is ruptured, permitting the expansion of the bag 12 and the webbing 13.
Operation of the air belt apparatus is as follows. When the acceleration sensor detects an acceleration not less than the predetermined value due to the crash of the motor vehicle, the inflator 11 is ignited and high-pressure gas is generated. The generated gas is supplied to the bag 12 of the shoulder belt 6 through a buckle housing 14 and the bag 12 is thereby expanded. When the bag 12 is expanded, the webbing 13 is expanded by pressure and thereby the entire shoulder belt 6 is expanded. As described above, when the shoulder belt 6 is expanded an area of the shoulder belt 6 contacting the chest region of an occupant increases at a greater rate than the expansion of the shoulder belt, permitting the occupant to be more softly restrained.
As described above, when the bag 12 is expanded, because the stitching thread 28 is automatically ruptured by means of the expansion force, the shoulder belt 6 is not substantially restrained from freely expanding by the stitching thread 28.